1. Field of the Invention
This invention relates generally to a punch press tool, and, in particular, to an IC chip fabrication punch press tool capable of cutting and removing material of relatively small dimensions.
2. Description of the Related Art
A punch press is a device used to cut a hole of predetermined size in a workpiece, often sheet metal. (See FIG. 1.) A punch press typically consists of a punch 1 and a die 2, which are often fabricated from hardened steel or steel alloy. The end of the punch 1, called the punch face 3, and the edge of the opening 4 of the die are sharpened so that on the down stoke of the punch 1, the punch face 3 contacts and pushes through a workpiece 5 into the die opening, thereby cutting a hole in the workpiece 5 in the size and shape of the punch 1 and die 2. (See FIGS. 2-4.) The piece of sheet metal or other material that is cut from the workpiece during the operation of the punch press is called a xe2x80x9cslugxe2x80x9d 6.
xe2x80x9cSlug-pullingxe2x80x9d is a recurring problem in the operation of high-speed punch presses, particularly in the computer chip fabrication process. Slug-pulling refers to the tendency of a slug 6 to follow or adhere to the punch face 3 during the return stroke of the punch 1 and to lodge at or near the plane of the workpiece 5 or die opening 4, thereby creating a variety of problems as the workpiece 5 is moved quickly past the punch 1 and die 2 in subsequent punching operations. Slug-pulling can reduce the efficiency of punch press operations, thereby resulting in reduced throughput, lower yields, and higher manufacturing costs.
Punch press manufacturers have adopted various means to retard or prevent slug-pulling. One solution involves carving a groove 7 in the inside surface of the die 2, with the groove 7 extending in the direction of movement of the reciprocating punch 1. (See FIG. 5.) The slug formed by such a die 2 will tend to become jammed against the inside surface of the die 2 and will not adhere to the punch face 3 as the punch 1 is retracted from the die 2. Because of the difficulty and expense involved in machining a groove 7 on the inside surface of the die 2, particularly a die 2 of relatively small dimensions, this solution has not proved satisfactory.
Another solution involves adding a protrusion 8 to the inside surface of the die 2, with the protrusion 8 extending toward the center of the die 2. (See FIG. 6.) A slug formed by such a die 2 will tend to be retained by the protrusion 8. Once again, because of the difficulty and expense involved in forming such a protrusion 8 on the inside surface of the die 2, particularly a die 2 with relatively small dimensions, this solution to the slug-pulling problem has not gained wide popularity.
Accordingly, it is a principle object and advantage of the present invention to overcome some or all of these limitations and to provide an improved slug-retaining punch press tool.
In accordance with one embodiment, the present invention comprises a punch press for removing dambars from the leadframe of an IC chip package. One or more irregularities are formed on the edge of the die face of the dambar die so that the dambar that is cut and removed by the operation of the punch press will have one or more burrs on its perimeter. In another embodiment, the edge of the die face has a plurality of irregularities. In still another embodiment, the irregularities are V-shaped grooves of specific dimensions. In yet another embodiment, two V-shaped grooves are formed symmetrically, at opposite edges of the die face.
In another embodiment, the present invention comprises a punch and die, the die having one or more irregularities at its opening perimeter so that the slug that is cut and removed by the operation of the punch press will have one or more burrs on its edge. In another embodiment, the opening perimeter of the die has a plurality of irregularities. In still another embodiment, the irregularities are grooves.
In another embodiment, the present invention comprises a punch and die that conform at all locations along their respective perimeters, except at one or more locations at which they do not conform. The locations at which they do not conform are shaped so that the slug that is cut and removed by the operation of the punch and die will have a burr on its perimeter.
In one embodiment, a method comprises forming a punch and die with an irregularity on the die face of the die, placing a sheet of material between the punch and die, pressing the punch through the material and into the opening of the die thereby cutting and removing a slug with a burr on its edge, retracting the punch from the die, and using the burr to prevent the slug from adhering to and following the punch as it is retracted from the die. In another embodiment, the method comprises forming a plurality of irregularities on the die face.
In another embodiment, a method comprises forming a punch and die with an irregularity on the die face of the die and employing the punch and die to cut a slug from a sheet of material with a burr on its edge so that the burr will prevent the slug from adhering to and following the punch as it is retracted from the die. In another embodiment, the method comprises forming a plurality of irregularities on the die face.
In another embodiment, a method comprises pressing a punch face through a sheet of material and forming a burr of the edge of the slug thereby cut from the material, which burr lodges against the smooth surface of the opening of the die and prevents the slug from adhering to and following the punch as it is retracted from the die. In another embodiment, the method comprises forming a plurality of burrs on the slug.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment disclosed.